Abstract: The purpose of this study is to model the caisson in clay from a complete finite element analysis to a simplified microelement modeling. First, the finite element method is used to analyze the caisson foundation in clay under different monotonic combined loadings. To ensure the reliability of the simulation results, the hardened soil model (HS) is adopted to simulate the normally consolidated clay. The effectiveness of the finite element analysis using the HS model is verified through comparing with centrifugal tests, and the swipe tests with radial displacement control is further extended to the study of failure modes in V-H-M (vertical force-horizontal force-bending moment) space. A three-dimensional failure envelope formula for the caisson foundation in clay in V-H-M space is proposed. Then, using this three-dimensional failure envelope formula, a macroelement design model for the caisson foundation in clay is proposed using a hypoplastic framework. By comparing with the experimental results, the validity of the strength and deformation response of the caisson foundation under simulated monotonic and cyclic loading conditions are verified. The proposed macroelement based model is practically useful in marine geotechnical design.

Key words: caisson foundation, failure envelope, clay, finite element method, cyclic loading, macro-element